Monoalkylated hydroquinones, resorcinols and catechols are generally difficult to prepare in high purity due to the complex separation of mono-, di- and unalkylated dihydroxybenzenes. To minimize this problem, usually low conversions are required which are an important factor in the cost of manufacture.
Monosubstituted dihydroxybenzenes are well known as polymerization inhibitors and as antioxidants. The monomethyl ether of hydroquinone is of significant economic importance. On the other hand, the use of compounds such as methyl 2-(4-hydroxyphenoxy)propionate has been described in the patent literature as a building block to prepare a wide range of biologically active materials, especially herbicides. See, for example, European Pat. No. 483 and British Patent Specification Nos. 1,599,121 and 1,550,574.
Japanese Patent Publications Nos. 55-127,331; 55-127,332; 55-127,333 and 55-127,334 to Ihara Chemical Industry, describe the preparation of monosubstituted hydroquinones by reacting the dimer of p-isopropenyl-phenol (4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene) with aromatic halides, ArX, where Ar is (substituted) phenyl, pryidyl or diazinyl and X is halide, to afford aromatic phenyl ethers. These materials are then thermally cracked to produce aromatic ethers of p-isopropenylphenol, which are then oxidized with H.sub.2 O.sub.2 or alkyl hydroperoxide in the presence of acid to give monosubstituted hydroquinones.
U.S. Pat. No. 4,328,361 to Upjohn describes the preparation of monosubstituted hydroquinones by reacting the dimer of p-isopropenylphenol with alkyl halides, followed by reaction of these products with HCl gas to afford 4-(1-chloro-1-methylethyl)phenyl ethers. These materials give monosubstituted hydroquinones when reacted with H.sub.2 O.sub.2 or alkyl hydroperoxide.
It is known that p-isopropenylphenol (p-IPP) can be alkylated under a variety of conditions with certain alkylating agents. For example, the alkylation of p-IPP with excess allyl chloride has been taught in Azerbaidzbanskii Khimicheskii Zhurnal, No. 6, pp. 52-57 (1979). Another example is the reaction of o-IPP with excess epichlorohydrin in Italian Pat. No. 705,414. Further examples involve the alkylation of p-IPP with various aromatic halides as in Japanese Kokai Tokkyo Koho No. 56-166138.
It is also known that isopropenylbenzenes containing no substituents whose reactivity could complicate the reaction can be oxidized to phenols using hydrogen peroxide and a strong acid catalyst. See German No. 2,214,971 to Upjohn.
However, the known art does not disclose or suggest alkylations of isopropenylphenols and subsequent oxidations of the isopropenylphenyl ethers where the alkylating agent is not an aromatic halide. When the alkylating agent is an aliphatic halide, sometimes it can be sensitive to hydrolysis and dehydrochlorination in competition with alkylation. Similarly, the ether moiety in aliphatic isopropenylphenyl ethers can be sensitive to oxidation or hydrolysis in competition with oxidation of the isopropenyl moiety. By comparison, all of these complications are not present in aromatic ethers of isopropenylphenol.